Composition of solvents in coatings

Because the requirements of the coating on solvents are more stringent, taking into account the volatility rate, solubility and cost and other factors, a single solvent is difficult to meet the requirements of the use of coatings, paint solvents are generally mixed solvents, composed of three parts, namely real solvents, solvents and thinners. Generally speaking, the composition of mixed solvents is controlled by its construction process conditions, such as coating drying temperature and drying time. A coating that is normally physically dry at room temperature and consists of 45% low boiling solvent, 45% medium boiling solvent, and 10% high boiling solvent

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the ratio of true solvent to inert solvent in the formulation should be appropriate in order to obtain a transparent, lightless coating. The solvent at the low boiling point accelerates drying, while the solvent at the medium boiling point and the high boiling point ensures that the film is film-free. Drying paint, baking magnetic paint and coil coating construction temperature is relatively high, so its solvent composition of high boiling point solvent content should be correspondingly high, containing only a small amount of volatile solvent, because volatile solvent will make the paint in the baking process "boiling".
, the nature of the solvent also depends on the type of resin. In order to obtain fast-drying, low solvent residue coating film, the solubility parameters of the mixed solvent and its hydrogen bond parameters must be located in the boundary part of the resin solubility range. On the other hand, these parameters of the mixed solvent must be similar to the parameters of the resin in order to ensure the satisfactory flow of the coating. It is difficult to find such a realistic balance and requires a lot of experimentation. According to the theory of solubility parameters, the non-solvent is more volatile than the real solvent in the selected mixed solvent, which is beneficial for accelerated drying. True solvents evaporate later in the coating film, increasing the fluidity of the coating. That is, with the evaporation of the solvent, the solubility parameters of the mixed solvent should be migrated from the boundary area of the resin solubility to the central area. However, it should be noted that during the evaporation of solvents, the increasing concentration of solids and the increase or decrease in the temperature of the coating will change the dissolved area of the resin.